Birth group | Morning cortisol | Evening cortisol | Mean daily cortisol | Diurnal slope | ||||

Geometric mean±SD* | Geometric mean±SD* | Geometric mean±SD* | Estimate of group effect Percentage (95% CI)† | P value | Geometric mean±SD‡ | Estimated group differences in cortisol slope Percentage (95% CI)† | P value | |

Term (≥37 weeks), n=42 | 7.8±2.6 | 1.7±2.3 | 3.6±1.8 | Reference | 4.6±3.9 | Reference | ||

Preterm (≤32 weeks), n=48 | 4.1±2.4 | 1.7±2.6 | 2.7±1.8 | −26.8 (−44.1 to −4.3) | 0.02 | 2.3±3.9 | −48.8 (−69.8 to −13.2) | 0.01 |

Extremely preterm (<28 weeks), n=14 | 4.3±2.4 | 3.5±2.4 | 3.9±1.7 | 13.3 (−22.8 to 66.3) | 0.52 | 1.2±3.8 | −72.9 (−87.1 to −42.8) | <0.001 |

Very preterm (28–32 weeks), n=34 | 4.0±2.4 | 1.3±2.3 | 2.3±1.8 | −36.6 (−52.4 to −15.6) | 0.002 | 3.0±3.6 | −33.6 (−62.0 to 16.0) | 0.15 |

Analyses were conducted using log

_{10}-transformed cortisol values.*Mean morning, evening and daily log

_{10}cortisol values were back-transformed producing geometric means.†Back-transformed regression coefficients represent percentage differences in cortisol metrics between groups.

‡ Diurnal slope representing the ratio of morning and evening geometric means was calculated through back transformation of mean log

_{10}(morning / evening) cortisol values.